#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb/stb_image.h>

#include "core/Shader.h"

#include <iostream>
#include <algorithm>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include "core/Camera.h"
#include <random>
#include "model/Model.h"

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow* window);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
unsigned int loadTexture(char const* path, bool gammaCorrection, bool bFlipV);
void renderCube();
void renderQuad();

float ourLerp(float a, float b, float f);


// basic settings
const unsigned int SCR_WIDTH = 800, SCR_HEIGHT = 600;
float deltaTime = 0.0f; // 当前帧与上一帧的时间差
float lastFrame = 0.0f; // 上一帧的时间

// camera
Camera camera = Camera(glm::vec3(4.82175, 4.09732, -4.28468), 141.1, -26.2001);
float cameraNearPlane = 0.1f;
float cameraFarPlane = 500.0f;
float lastX = 400, lastY = 300;

// render var
unsigned int quadVAO = 0, quadVBO = 0;
unsigned int cubeVAO = 0, cubeVBO = 0;

// lighting info
// -------------
glm::vec3 lightPos = glm::vec3(2.0, 4.0, -2.0);
glm::vec3 lightColor = glm::vec3(0.2, 0.2, 0.7);

unsigned int gScrrenTextureNum = 8;
unsigned int gScrrenTextureIndex = 6;
bool bToggleGBufferKeyPressed = false;
bool bRenderSpecular = false;

int main()
{
	// glfw: initialize and configure
	// ------------------------------
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

	// glfw window creation
	// --------------------
	GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
	if (window == NULL)
	{
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
	glfwSetCursorPosCallback(window, mouse_callback);
	glfwSetScrollCallback(window, scroll_callback);

	// tell GLFW to capture our mouse
	glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

	// glad: load all OpenGL function pointers
	// ---------------------------------------
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}

	// configure global opengl state
	// -----------------------------
	glEnable(GL_DEPTH_TEST);

	// build and compile shaders
	// -------------------------
	Shader gBufferShader("shader/gbuffer.vert", "shader/gbuffer.frag");
	Shader screenShader("shader/screen.vert", "shader/screen.frag");
	Shader ssaoShader("shader/SSAO.vert", "shader/SSAO.frag");
    Shader ssaoBlurShader("shader/SSAOBlur.vert", "shader/SSAOBlur.frag");
	Shader lightingShader("shader/shader.vert", "shader/shader.frag");

	Model backpack("backpack/backpack.obj");

	unsigned int cubeDiffuse = loadTexture("resource/container2.png", false, false);
	unsigned int cubeSpecular = loadTexture("resource/container2_specular.png", false, false);

	// configure g-buffer framebuffer
	// ------------------------------
	unsigned int gBuffer;
	glGenFramebuffers(1, &gBuffer);
	glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
	unsigned int gPosition, gNormal, gAlbedoSpec;
	// position color buffer
	glGenTextures(1, &gPosition);
	glBindTexture(GL_TEXTURE_2D, gPosition);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, gPosition, 0);
	// normal color buffer
	glGenTextures(1, &gNormal);
	glBindTexture(GL_TEXTURE_2D, gNormal);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, gNormal, 0);
	// color + specular color buffer
	glGenTextures(1, &gAlbedoSpec);
	glBindTexture(GL_TEXTURE_2D, gAlbedoSpec);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT2, GL_TEXTURE_2D, gAlbedoSpec, 0);
	// tell OpenGL which color attachments we'll use (of this framebuffer) for rendering 
	unsigned int attachments[3] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
	glDrawBuffers(3, attachments);
	// create and attach depth buffer (renderbuffer)
	unsigned int rboDepth;
	glGenRenderbuffers(1, &rboDepth);
	glBindRenderbuffer(GL_RENDERBUFFER, rboDepth);
	glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT);
	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rboDepth);
	// finally check if framebuffer is complete
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "Framebuffer not complete!" << std::endl;
	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// also create framebuffer to hold SSAO processing stage 
	// -----------------------------------------------------
	unsigned int ssaoFBO, ssaoBlurFBO;
	glGenFramebuffers(1, &ssaoFBO);  glGenFramebuffers(1, &ssaoBlurFBO);
	glBindFramebuffer(GL_FRAMEBUFFER, ssaoFBO);
	unsigned int ssaoColorBuffer, ssaoColorBufferBlur;
	// SSAO color buffer
	glGenTextures(1, &ssaoColorBuffer);
	glBindTexture(GL_TEXTURE_2D, ssaoColorBuffer);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, SCR_WIDTH, SCR_HEIGHT, 0, GL_RED, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, ssaoColorBuffer, 0);
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "SSAO Framebuffer not complete!" << std::endl;
	// and blur stage
	glBindFramebuffer(GL_FRAMEBUFFER, ssaoBlurFBO);
	glGenTextures(1, &ssaoColorBufferBlur);
	glBindTexture(GL_TEXTURE_2D, ssaoColorBufferBlur);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, SCR_WIDTH, SCR_HEIGHT, 0, GL_RED, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, ssaoColorBufferBlur, 0);
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "SSAO Blur Framebuffer not complete!" << std::endl;
	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// 光照阶段结果
	// ----------------------------------------------------------------
	unsigned int lightingFBO;
    glGenFramebuffers(1, &lightingFBO);
    glBindFramebuffer(GL_FRAMEBUFFER, lightingFBO);
	unsigned int lightingColorBuffer;
    glGenTextures(1, &lightingColorBuffer);
    glBindTexture(GL_TEXTURE_2D, lightingColorBuffer);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, lightingColorBuffer, 0);
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "SSAO Blur Framebuffer not complete!" << std::endl;
	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// generate sample kernel
	// ----------------------
	std::uniform_real_distribution<GLfloat> randomFloats(0.0, 1.0); // generates random floats between 0.0 and 1.0
	std::default_random_engine generator;
	std::vector<glm::vec3> ssaoKernel;
	for (unsigned int i = 0; i < 64; ++i)
	{
		glm::vec3 sample(randomFloats(generator) * 2.0 - 1.0, randomFloats(generator) * 2.0 - 1.0, randomFloats(generator));
		sample = glm::normalize(sample);
		sample *= randomFloats(generator);
		float scale = float(i) / 64.0f;

		// scale samples s.t. they're more aligned to center of kernel
		scale = ourLerp(0.1f, 1.0f, scale * scale);
		sample *= scale;
		ssaoKernel.push_back(sample);
	}

	// generate noise texture
	// ----------------------
	std::vector<glm::vec3> ssaoNoise;
	for (unsigned int i = 0; i < 16; i++)
	{
		glm::vec3 noise(randomFloats(generator) * 2.0 - 1.0, randomFloats(generator) * 2.0 - 1.0, 0.0f); // rotate around z-axis (in tangent space)
		ssaoNoise.push_back(noise);
	}
	unsigned int noiseTexture; glGenTextures(1, &noiseTexture);
	glBindTexture(GL_TEXTURE_2D, noiseTexture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, 4, 4, 0, GL_RGB, GL_FLOAT, &ssaoNoise[0]);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

	screenShader.use();
	screenShader.setInt("screenTexture", 0);
	lightingShader.use();
	lightingShader.setInt("gPosition", 0);
	lightingShader.setInt("gNormal", 1);
	lightingShader.setInt("gAlbedo", 2);
	lightingShader.setInt("ssao", 3);
	ssaoShader.use();
	ssaoShader.setInt("gPosition", 0);
	ssaoShader.setInt("gNormal", 1);
	ssaoShader.setInt("texNoise", 2);
	ssaoBlurShader.use();
    ssaoBlurShader.setInt("ssaoInput", 0);

	// render loop
	// -----------
	while (!glfwWindowShouldClose(window))
	{
		std::string title = "LearnOpenGL";
		std::string renderTextureState;
		if (gScrrenTextureIndex == 0)
		{
			renderTextureState = "Position";
		}
		else if (gScrrenTextureIndex == 1)
		{
			renderTextureState = "Normal";
		}
		else if (gScrrenTextureIndex == 2)
		{
			renderTextureState = "Diffuse";
		}
		else if (gScrrenTextureIndex == 3)
		{
			renderTextureState = "Specular";
		}
		else if (gScrrenTextureIndex == 4)
		{
            renderTextureState = "SSAO";
		}
		else if (gScrrenTextureIndex == 5)
		{
            renderTextureState = "SSAO Blur";
		}
		else if (gScrrenTextureIndex == 6)
		{
            renderTextureState = "Final With SSAO";
		}
		else if (gScrrenTextureIndex == 7)
		{
            renderTextureState = "Final Without SSAO";
		}

		glfwSetWindowTitle(window, ("LearnOpenGL    Render:" + renderTextureState).c_str());


		// per-frame time logic
		// --------------------
		float currentFrame = static_cast<float>(glfwGetTime());
		deltaTime = currentFrame - lastFrame;
		lastFrame = currentFrame;

		// input
		// -----
		processInput(window);

		// 1. geometry pass: render scene's geometry/color data into gbuffer
		// -----------------------------------------------------------------
		glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 50.0f);
		glm::mat4 view = camera.GetViewMatrix();
		glm::mat4 model = glm::mat4(1.0f);
		gBufferShader.use();
		gBufferShader.setMat4("projection", projection);
		gBufferShader.setMat4("view", view);
		// room cube
		model = glm::mat4(1.0f);
		model = glm::translate(model, glm::vec3(0.0, 7.0f, 0.0f));
		model = glm::scale(model, glm::vec3(7.5f, 7.5f, 7.5f));
		gBufferShader.setMat4("model", model);
		gBufferShader.setInt("invertedNormals", 1); // invert normals as we're inside the cube
		glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, cubeDiffuse);
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, cubeSpecular);
		renderCube();
		gBufferShader.setInt("invertedNormals", 0);
		// backpack model on the floor
		model = glm::mat4(1.0f);
		model = glm::translate(model, glm::vec3(0.0f, 0.5f, 0.0));
		model = glm::rotate(model, glm::radians(-90.0f), glm::vec3(1.0, 0.0, 0.0));
		model = glm::scale(model, glm::vec3(1.0f));
		gBufferShader.setMat4("model", model);
		backpack.Draw(gBufferShader);
		glBindFramebuffer(GL_FRAMEBUFFER, 0);


		// 2. generate SSAO texture
		// ------------------------
		glBindFramebuffer(GL_FRAMEBUFFER, ssaoFBO);
		glClear(GL_COLOR_BUFFER_BIT);
		ssaoShader.use();
		// Send kernel + rotation 
		for (unsigned int i = 0; i < 64; ++i)
			ssaoShader.setVec3("samples[" + std::to_string(i) + "]", ssaoKernel[i]);
		ssaoShader.setMat4("projection", projection);
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, gPosition);
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, gNormal);
		glActiveTexture(GL_TEXTURE2);
		glBindTexture(GL_TEXTURE_2D, noiseTexture);
		renderQuad();
		glBindFramebuffer(GL_FRAMEBUFFER, 0);


		// 3. blur SSAO texture to remove noise
		// ------------------------------------
		glBindFramebuffer(GL_FRAMEBUFFER, ssaoBlurFBO);
		glClear(GL_COLOR_BUFFER_BIT);
		ssaoBlurShader.use();
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, ssaoColorBuffer);
		renderQuad();
		glBindFramebuffer(GL_FRAMEBUFFER, 0);

		// 4. lighting pass
		// --------------------------------------
		glBindFramebuffer(GL_FRAMEBUFFER, lightingFBO);
		glClear(GL_COLOR_BUFFER_BIT);
        lightingShader.use();
		glm::vec3 lightPosView = glm::vec3(camera.GetViewMatrix() * glm::vec4(lightPos, 1.0));
		lightingShader.setVec3("light.Position", lightPosView);
		lightingShader.setVec3("light.Color", lightColor);
		// Update attenuation parameters
		const float linear = 0.09f;
		const float quadratic = 0.032f;
		lightingShader.setFloat("light.Linear", linear);
		lightingShader.setFloat("light.Quadratic", quadratic);
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, gPosition);
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, gNormal);
		glActiveTexture(GL_TEXTURE2);
		glBindTexture(GL_TEXTURE_2D, gAlbedoSpec);
		glActiveTexture(GL_TEXTURE3); // add extra SSAO texture to lighting pass
		glBindTexture(GL_TEXTURE_2D, ssaoColorBufferBlur);
        lightingShader.setBool("bUseSSAO", gScrrenTextureIndex != 7);
		renderQuad();
        glBindFramebuffer(GL_FRAMEBUFFER, 0);

		// 5.将数据渲染到屏幕上
		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        screenShader.use();
		glActiveTexture(GL_TEXTURE0);
		unsigned int renderTextureIndex = 0;
		switch (gScrrenTextureIndex)
		{
		case 0:
			renderTextureIndex = gPosition;
			break;
		case 1:
			renderTextureIndex = gNormal;
			break;
		case 2:
			renderTextureIndex = gAlbedoSpec;
			break;
		case 3:
			renderTextureIndex = gAlbedoSpec;
			bRenderSpecular = true;
			break;
		case 4:
			renderTextureIndex = ssaoColorBuffer;
		case 5:
            renderTextureIndex = ssaoColorBufferBlur;
			break;
		case 6:
            renderTextureIndex = lightingColorBuffer;
			break;
		case 7:
			renderTextureIndex = lightingColorBuffer;
			break;
		}
		glBindTexture(GL_TEXTURE_2D, renderTextureIndex);
        screenShader.setBool("bRenderSpecular", bRenderSpecular);
		renderQuad();
		bRenderSpecular = false;

		// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
		// -------------------------------------------------------------------------------
		glfwSwapBuffers(window);
		glfwPollEvents();
	}

	// optional: de-allocate all resources once they've outlived their purpose:
	// ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteBuffers(1, &cubeVBO);
    glDeleteVertexArrays(1, &quadVAO);
    glDeleteBuffers(1, &quadVBO);
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteBuffers(1, &cubeVBO);

	glfwTerminate();
	return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow* window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
	{
		glfwSetWindowShouldClose(window, true);
	}
	else if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::FORWARD, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::BACKWARD, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::LEFT, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::RIGHT, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_Q) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::UP, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_E) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::DOWN, deltaTime);

	if (glfwGetKey(window, GLFW_KEY_RIGHT) == GLFW_PRESS && !bToggleGBufferKeyPressed)
	{
		gScrrenTextureIndex = (gScrrenTextureIndex + 1) % gScrrenTextureNum;
		bToggleGBufferKeyPressed = true;
	}
	else if (glfwGetKey(window, GLFW_KEY_LEFT) == GLFW_PRESS && !bToggleGBufferKeyPressed)
	{
        gScrrenTextureIndex = (gScrrenTextureIndex + gScrrenTextureNum - 1) % gScrrenTextureNum;
        bToggleGBufferKeyPressed = true;
	}
    if (glfwGetKey(window, GLFW_KEY_RIGHT) == GLFW_RELEASE && glfwGetKey(window, GLFW_KEY_LEFT) == GLFW_RELEASE)
	{
		bToggleGBufferKeyPressed = false;
	}

	if (glfwGetKey(window, GLFW_KEY_P) == GLFW_PRESS)
	{
		std::cout << "Position: " << camera.Position.x << ", " << camera.Position.y << ", " << camera.Position.z << "" <<std::endl;
		std::cout << "Rotation: " << camera.Yaw << ", " << camera.Pitch << "" << std::endl;
	}
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	// make sure the viewport matches the new window dimensions; note that width and 
	// height will be significantly larger than specified on retina displays.
	glViewport(0, 0, width, height);
}

void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
	static bool firstMouse = true;
	if (firstMouse) // 这个bool变量初始时是设定为true的
	{
		lastX = xpos;
		lastY = ypos;
		firstMouse = false;
	}

	float xoffset = xpos - lastX;
	float yoffset = lastY - ypos; // 注意这里是相反的，因为y坐标是从底部往顶部依次增大的
	lastX = xpos;
	lastY = ypos;

	camera.ProcessMouseMovement(xoffset, yoffset);
}

void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
	camera.ProcessMouseScroll(yoffset);
}

unsigned int loadTexture(char const* path, bool gammaCorrection, bool bFlipV)
{
	unsigned int textureID;
	glGenTextures(1, &textureID);

	int width, height, nrComponents;
	if (bFlipV)
	{
        stbi_set_flip_vertically_on_load(true);
	}
	unsigned char* data = stbi_load(path, &width, &height, &nrComponents, 0);
	if (data)
	{
		GLenum internalFormat;
		GLenum dataFormat;
		if (nrComponents == 1)
		{
			internalFormat = dataFormat = GL_RED;
		}
		else if (nrComponents == 3)
		{
			internalFormat = gammaCorrection ? GL_SRGB : GL_RGB;
			dataFormat = GL_RGB;
		}
		else if (nrComponents == 4)
		{
			internalFormat = gammaCorrection ? GL_SRGB_ALPHA : GL_RGBA;
			dataFormat = GL_RGBA;
		}

		glBindTexture(GL_TEXTURE_2D, textureID);
		glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, dataFormat, GL_UNSIGNED_BYTE, data);
		glGenerateMipmap(GL_TEXTURE_2D);

		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

		stbi_image_free(data);
	}
	else
	{
		std::cout << "Texture failed to load at path: " << path << std::endl;
		stbi_image_free(data);
	}

	stbi_set_flip_vertically_on_load(false);

	return textureID;
}

void renderCube()
{
	// initialize (if necessary)
	if (cubeVAO == 0)
	{
		float vertices[] = 
		{
			// back face
			-1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
			 1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
			 1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 0.0f, // bottom-right         
			 1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
			-1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
			-1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 1.0f, // top-left
			// front face
			-1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
			 1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 0.0f, // bottom-right
			 1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
			 1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
			-1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 1.0f, // top-left
			-1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
			// left face
			-1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
			-1.0f,  1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-left
			-1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
			-1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
			-1.0f, -1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-right
			-1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
			// right face
			 1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
			 1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
			 1.0f,  1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-right         
			 1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
			 1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
			 1.0f, -1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-left     
			 // bottom face
			 -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
			  1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 1.0f, // top-left
			  1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
			  1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
			 -1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 0.0f, // bottom-right
			 -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
			 // top face
			 -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
			  1.0f,  1.0f , 1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
			  1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 1.0f, // top-right     
			  1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
			 -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
			 -1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 0.0f  // bottom-left        
		};
		glGenVertexArrays(1, &cubeVAO);
		glGenBuffers(1, &cubeVBO);
		// fill buffer
		glBindBuffer(GL_ARRAY_BUFFER, cubeVBO);
		glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
		// link vertex attributes
		glBindVertexArray(cubeVAO);
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
		glEnableVertexAttribArray(2);
		glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
		glBindBuffer(GL_ARRAY_BUFFER, 0);
		glBindVertexArray(0);
	}
	// render Cube
	glBindVertexArray(cubeVAO);
	glDrawArrays(GL_TRIANGLES, 0, 36);
	glBindVertexArray(0);
}

void renderQuad()
{
	if (quadVAO == 0)
	{
		float quadVertices[] = 
		{
			// positions        // texture Coords
			-1.0f,  1.0f, 0.0f, 0.0f, 1.0f,
			-1.0f, -1.0f, 0.0f, 0.0f, 0.0f,
			 1.0f,  1.0f, 0.0f, 1.0f, 1.0f,
			 1.0f, -1.0f, 0.0f, 1.0f, 0.0f,
		};
		// setup plane VAO
		glGenVertexArrays(1, &quadVAO);
		glGenBuffers(1, &quadVBO);
		glBindVertexArray(quadVAO);
		glBindBuffer(GL_ARRAY_BUFFER, quadVBO);
		glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), &quadVertices, GL_STATIC_DRAW);
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
	}
	glBindVertexArray(quadVAO);
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
	glBindVertexArray(0);
}

float ourLerp(float a, float b, float f)
{
	return a + f * (b - a);
}
